The present invention is related to radio frequency (RF) power filters. In particular, the present invention is related to RF power filters for use in plasma processing systems.
Plasma processing systems, such as capacitively coupled plasma (CCP) systems, inductively coupled plasma (ICP) systems, and transformer coupled plasma (TCP) systems, are employed in various industries for fabricating devices on wafers. For example, the industries may include semiconductor, magnetic read/write and storage, optical system, and micro-electromechanical system (MEMS) industries.
A plasma processing system may generate and sustain plasma in a plasma processing chamber to perform etching and/or deposition on a wafer such that device features may be formed on the wafer. The plasma processing system may include an electrostatic chuck (ESC) for supporting the wafer during one or more plasma processing processes. An ESC with zone-to-zone tunable temperature capability may be critical for temperature sensitive plasma processing processes. For minimizing electromagnetic compatibility (EMC) failure, interference issues, and power loss issues that may be caused by RF power transmitted from the ESC and leaked from the plasma processing chamber, an RF power filter may be implemented in the plasma processing system.
FIG. 1A shows a schematic representation illustrating several components of a plasma processing system 100. Plasma processing system 100 may include an ESC 108 that may support a wafer (well known in the art and not shown in this figure) during plasma processing of the wafer. In addition, ESC 108 may also serve as a lower electrode; ESC 108 may receive RF power supplied through an RF feed 120 for generating and/or sustaining plasma between ESC 108 and an upper electrode (well known in the art and not shown in this figure) for performing plasma processing.
ESC 108 may be a tunable ESC (TESC) capable of two-zone tunable temperature control. The temperature tuning capability of ESC 108 may be achieved by implementing two electric heating elements (well known in the art and not shown in the figure) embedded under the ceramic puck on top of ESC 108, one electric heating element being implemented for each of the two zones.
The two electric heating elements may be powered by alliterating currents (ACs) supplied by an AC power supply (well known in the art and not shown in the figure) through an AC connector 138, an RF power filter 102, a cable 104, and terminals 110a, 110b, 110c, and 110d. Two of terminals 110a, 110b, 110c, and 110d may be coupled to a first electric heating element of the two electric heating elements for powering the first electric heating element; the other two of terminals 110a, 110b, 110c, and 110d may be coupled to a second heating element of the two electric heating element for powering the second electric heating element. The temperature of each of the electric heating elements may be controlled in a bang-bang fashion with a zero crossing technique.
RF power filter 102 may transmit AC power for powering the electric heating elements. RF power filter 102 may also minimize or block RF power transmitted from ESC 108 to other components outside of plasma processing chamber body 106, for minimizing the abovementioned EMC failure issues, interference issues, and power loss issues.
Nevertheless, existing RF power filter designs may cause issues related to processing uniformity and performance consistency in plasma processing systems, as discussed with reference to the example of FIG. 1B.
FIG. 1B shows a schematic representation illustrating an example prior-art RF power filter 102 for use in a plasma processing system, such as plasma processing system 100 illustrated in the example of FIG. 1A. As illustrated in the example of FIG. 1B, RF power filter 102 may include an enclosure 150. RF power filter 102 may also include a core member 158 disposed inside enclosure 150. RF power filter 102 may also include a set of inductors 156 (including four inductors) formed by wire 166a, wire 166b, wire 166c, and wire 166d separately wound around and wound along a portion of core member 158. Wires 166a-166d may be connected through cable 104 (illustrated in the example of FIG. 1A) to terminals 110a-110d (illustrated in the example of FIG. 1A) for supplying AC power to the electric heaters. The set of inductors 156 (formed by wire 166a, wire 166b, wire 166c, and wire 166d, respectively) may be connected to a set of grounded capacitors 154 (including four capacitors) to form tuned circuits (or resonant circuits) to filter out or block RF power at the 60 MHz operating frequency transmitted from ESC 108 (illustrated in the example of FIG. 1A), for example, through cable 104 (illustrated in the example of FIG. 1A) and wires 166a-166d. 
Given that wire 166a, wire 166b, wire 166c, and wire 166d are separated by significant distances, there are significant differences in stray capacitances formed between wire 166a and walls of enclosure 150, stray capacitances formed between wire 166b and walls of enclosure 150, stray capacitances formed between wire 166c and walls of enclosure 150, and stray capacitances formed between wire 166d and walls of enclosure 150. For example, the stray capacitance formed between a section of wire 166a and a side wall of enclosure 150 may be significantly different from the stray capacitance formed between a corresponding section of wire 166b and the same side wall of enclosure 150. As a result, at ESC 108 (illustrated in the example of FIG. 1A), the impedance level at terminal 110a (connected to wire 166a), the impedance level at terminal 110b (connected to wire 166b), the impedance level at terminal 110c (connected to wire 166c), and the impedance level at terminal 110d (connected to wire 166d) may be significantly different from each other. Consequently, plasma processing rates (e.g., etch rates) may be substantially non-uniform or substantially inconsistent across the surface of a wafer disposed on ESC 108, and the manufacturing yield may be substantially undesirable.
Typically, wires 166a-166d may be polytetrafluoroethylene (PTFE) wires or wires coated with PTFE, and core member 158 also may be coated with PTFE, for minimizing contamination. PTFE typically has a low coefficient of friction; therefore, wires 166a-166d may tend to move away from specified positions with respect to core member 158. As a result, the abovementioned stray capacitances may substantially change, and plasma processing profiles (e.g., etching profiles) may be substantially inconsistent from wafer to wafer, from RF power filter to RF power filter, and/or from plasma processing chamber to plasma processing chamber even if system specifications and processing recipes remain unchanged. As a result, for achieving acceptable consistency in plasma processing, costly and time-consuming calibration processes performed by highly skillful workers may be required.
In addition, the tolerances (or acceptable deviations from specified values) of the capacitors in the set of grounded capacitors 154 also may contribute to substantial variation (or substantial inconsistency) in plasma processing profiles (e.g., etch profiles) on wafers, from RF power filter to RF power filter, and/or from plasma processing chamber to plasma processing chamber.
RF power filter 102 may also include a set of inductors 152 (including four inductors) formed by wire 162a, wire 162b, wire 162c, and wire 162d separately wound around and wound along a portion of core member 158. Wires 162a-162d may be connected through wires 166a-166d and cable 104 (illustrated in the example of FIG. 1A) to terminals 110a-110d (illustrated in the example of FIG. 1A) for supplying AC power to the electric heaters. The set of inductors 152 (formed by wire 162a, wire 162b, wire 162c, and wire 162d, respectively) may be connected to a set of grounded capacitors 174 (including four capacitors) to form tuned circuits to filter out or block RF power at the 27 MHz operating frequency transmitted from ESC 108 (illustrated in the example of FIG. 1A).
RF power filter 102 may also include another core member 178 disposed inside enclosure 150. RF power filter 102 may also include a set of inductors 172 (including four inductors) formed by wire 182a, wire 182b, wire 182c, and wire 182d separately wound around and wound along a portion of core member 178. Wires 182a-182d may be connected through a set of wires 180 and AC connecter 138 (illustrated in the example of FIG. 1A) to an AC power supply. Wires 182a-182d may be connected through wires 162a-162d, wires 166a-166d, cable 104 (illustrated in the example of FIG. 1A) to terminals 110a-110d (illustrated in the example of FIG. 1A) for supplying AC power to the electric heaters. The set of inductors 172 (formed by wire 182a, wire 182b, wire 182c, and wire 182d, respectively) may be connected to a set of grounded capacitors 176 (including four capacitors) to form tuned circuits to filter out or block RF power at the 2 MHz operating frequency transmitted from ESC 108 (illustrated in the example of FIG. 1A).
Analogous to the significant distances (or space) between wires 166a-166d, the significant distances (or space) between wires 162a-162d and the significant distances (or space) between wires 182a-182d also may contribute to substantially non-uniform plasma processing rates on wafers and a substantially undesirable manufacturing yield.
Analogous to the movement (and repositioning) of wires 166a-166d, the movement (and repositioning) of wires 162a-162d and the movement (and repositioning) of wires 182a-182d also may contribute to substantial variation or substantial inconsistency in plasma processing profiles (e.g., etching profiles) from wafer to wafer, from RF power filter to RF power filter, and/or from plasma processing chamber to plasma processing chamber.
In addition, analogous to the tolerances of the capacitors in the set of grounded capacitors 154, the tolerances of the capacitors in the set of grounded capacitors 174 and the tolerances of the capacitors in the set of grounded capacitors 176 also may contribute to substantial variation (or substantial inconsistency) in plasma processing profiles on wafers, from RF power filter to RF power filter, and/or from plasma processing chamber to plasma processing chamber.